Long range studies on the in vitro bioactivity of luteninizing hormone and chorionic gonadotropin in man and other species were continued. The recently developed in vitro bioassay for the measurement of LH and hCG in serum has been more extensively applied to studies on gonadotropin regulation in man and other species. Stimulation of humans with LHRH has provided new information about the occurrence of qualitative changes in the LH molecule at different stages of the menstrual cycle, and after the menopause. The application of RICT assay to the measurement of monkey LH has been validated and applied to physiological studies which will form the basis for further endocrine investigation of gonadotropin regulation in the species. BIBLIOGRAPHIC REFERENCES: Dufau, M.L., Beitius, I.Z., McArthur, J.W. and Catt, K.J.: Qualitative Differences of Serum LH - the Testis in Normal and Infertile Men. (Eds.: Troen, P. and Nankin, H.) Raven Press, p. 309, 1977. N.Y. Dufau, M.L., and Catt, K.J.: Separation of Glycoprotein Hormones with Agarose-Concanavalin A. -Concanavalin A as a Tool. (Bittiger, H. and Schnebli, H.P.) John Wiley and Sons. New York, p. 585, 1977.